Lactoferrin is an 80 kD iron-binding glycoprotein present in most exocrine fluids, including tears, bile, bronchial mucus, gastrointestinal fluids, cervico-vaginal mucus, seminal fluid, and milk. It is a major constituent of the secondary specific granules of circulating poly-morphonuclear neutrophils. The richest source of lactoferrin is mammalian milk and colostrum.
Lactoferrin circulates at a concentration of 2-7 μg/ml. It has multiple postulated biological roles, including regulation of iron metabolism, immune function, and embryonic development. Lactoferrin has anti-microbial activity against a range of pathogens including Gram positive and Gram negative bacteria, yeasts, and fungi. The anti-microbial effect of lactoferrin is based on its capability of binding iron, which is essential for the growth of the pathogens. Lactoferrin also inhibits the replication of several viruses and increases the susceptibility of some bacteria to antibiotics and lysozyme by binding to lipid A component of lipopolysaccharides on bacterial membranes.